St Nicholas, Grosmont, is a large church with a strong thirteenth-century character and more or less contemporary with the castle which was the centre of the lordship. The church served both the castle garrison and the new borough. It has an ambitious cruciform plan with a central tower. Much of the church was rebuilt in the 19th century, but the long, aisled nave was spared reconstruction and is a shock to the modern visitor who encounters an uncluttered medieval interior dominated by the arcades and roof.
The roof has an archaic character quite unlike any other surviving medieval roof in Wales although there are comparable examples in southern England. The bays are defined by very plain trusses of heavy scantling. Posts rise from tie-beam to lap-jointed collar and from collar to ridge; the trusses are impressively braced to a collar-purlin to prevent racking. This type of king-strut roof is rare and difficult to date with precision. While impressive, they belong to the period before the appreciation of the decorative possibilities of the heavily-bayed roof. Could it be that this roof dates back to the foundation of the church in the 13th century? If so, it would be the earliest surviving church roofs in Wales and one of the earliest in the United Kingdom. Tree-ring dating was commissioned to date the roof scientifically.
Sampling provided good independent dating evidence and gave a likely felling-date range of 1214-1244.